Does the steam version of blender install Python automatically?
Python is bundled with all versions of Blender, since 2.5 onwards. Many aspects of the UI are declared in python and it is therefor an integral part of the UI system (shipping without would be a world of hurt).

According to Make Human docs the add-on comes with its own version of Python ( 2.7 ). 


  (...) there is a bundled python inside the build zips (...)


This means you have at least two versions of python on your machine, one that Blender uses and one that Make Human uses, that's OK.